CROSS REFERENCE TO RELATED APPLICATIONS
This application is related to the following applications:
1. Active Hand Controller Feedback Loop, Ser. No. 07/957,278, now U.S. Pat. No. 5,264,768.
2. Rate Mode Hand Controller With Force Reflection, Ser. No. 08/149,018 which is a continuation of Ser. No. 07/715,825, now abandoned.
3. Position Dependent Rate Dampening in an Active Hand Controller, Ser. No. 07/957,427, now U.S. Pat. No. 5,347,204.
1. Field of the Invention
This invention relates to an improved, active, position mode hand controller, and more particularly to position mode hand controller with a synthetic friction algorithm suitable for use with static, and quasi static controllers. This invention can be used alone or in combination with other hand controller systems, such as, for example, those of the above-referenced co-pending applications.
The invention described herein was made in the performance of work under NASA Contract No. NAS9-18200 and is subject to the provisions of Section 305 of the National Aeronautics and Space (NASA) Act of 1958 (42 U.S.C. 2457). The invention described herein has been granted NASA Waiver Case No. W-2887.
2. Description of the Prior Art
Position mode hand controllers are used to control the position of a remote tool or object in accordance with movement by an operator of a hand-control element also referred to as a grip. A desirable characteristic of a position mode hand controller is to have the hand-control element stay in position when no force is applied to it. Similarly, it is also desirable that an operator easily be able to confine the movement of a hand-control element to movement along a single axis even though the element is capable of movement along more than one axis.
Friction in the prior art has been introduced into the controller system both in order to provide a force that tends to keep the hand-control element at a rest position when no force is applied and to keep an element moving along a single axis in response to a single axis input force.
In prior art passive hand controllers, friction is usually provided mechanically (see FIG. 1A and 1B). As shown in FIG. 1A, the movement of hand controller element (10) in either the (+) or (-) direction is mechanically linked to a position transducer (14) which generates an electrical signal that is input into a robotic controller 16 which acts upon the controlled element 20 via mechanical means. In such hand controller mechanical mechanizations, friction mechanisms are frequently provided which supply the feel characteristics illustrated in FIG. 1B. This model of friction, prior art documented in many publications, defines a static friction (sometimes called break away friction) and dynamic friction which decreases as a function of velocity between the sliding elements to a nominal constant. Mechanical friction can also be provided in so-called active position mode hand controllers (i.e., controllers with motor driven hand-control elements). In active hand controllers, introduction of mechanical friction is disadvantageous for several reasons. Mechanical friction in an active position mode controller increases power consumption and, hence, is inefficient. Further, a mechanical approach to the introduction of friction requires extra mechanical parts that in turn increase the size and weight of the controller and decrease its reliability.
Prior art proposals for active, position mode, hand controllers include simulating friction by means of the hand-control element drive motor. These prior art proposals are generally based on a model that assumes friction is a constant force opposing velocity. Here the velocity vector of the hand-control element is determined and the motor is controlled to produce a constant force (or add a constant force to an otherwise commanded force) in a direction opposite the velocity vector. This is either done in electronic hardware or with software. This approach is satisfactory for a dynamic hand controller application where the hand-control element constantly is in motion. It is not satisfactory, however, for static or quasi static application where the hand-control element is frequently at zero, or at near zero, velocity.